This invention relates to the field of waveform generators and more particularly to a device and method capable of simulating radar returns from precipitation. The purpose of simulating such returns is so that a weather radar receiver and its associated circuitry can be accurately calibrated and tested. Moreover, the device presented herein may be employed to generate various dynamic weather patterns for training purposes.
It is desirable to test and calibrate weather radar systems to insure that the device accurately depicts and displays the ambient weather conditions. It is from such a display that a pilot is made aware of the general weather conditions surrounding his aircraft. Based upon his assessement of the displayed conditions, various judgments regarding air traffic routes are made. A variety of simulators are currently available for testing and calibrating such systems. These simulators include both digital and analogue devices. Some are capable of providing various Doppler returns (U.S. Pat. No. 3,745,579) while other simulators provide returns from the operation of a plurality of radar transmitters (U.S. Pat. No. 3,792,475). Moreover, there are sophisticated simulators such as that disclosed by Goetz (U.S. Pat. No. 3,832,712) which are capable of providing general Doppler returns. The major drawback to these devices, as typified by Goetz, is that they require the use of expensive high speed digital computers.
Previously, methods of generating precipitation return signals have been limited and have generally employed the statistical properties of random noise to simulate the random nature of the precipitation returns from the many scatterers. The random noise was used to modulate an audio frequency signal, which signal represented the frequency shift due to precipitation particle velocity. The shifted signal was then used to modulate an intermediate frequency signal and the intermediate frequency signal was applied to the radar under test. Such a system does not accurately depict precipitation, is difficult to tune, requires a variety of test instruments, and is not suitable for nor does it retain its calibration.
With the above disadvantages in mind, I have invented a method for simulating precipitation as well as a method of generating frequency spectra.